Process for producing acrylic fibers

ABSTRACT

AN IMPROVEMENT IN CONVENTIONAL WET-SPINNING PROCEDURE FOR ACRYLIC FIBERS WHEREIN THE FIBERS ARE HEATED UNDER HIGH HUMIDITY CONDITIONS TO OBTAIN AN INCREASE IN BONDED WATER AND A RESULTING INCREASE IN ELASTIC RECOVERY PROPERTIES.

8, 1974 HIDETO SEKIGUCH! ET AL 3,

PROCESS FDR PRODUCING ACRYLIC FIBERS Filed June 8, 1971 2 Shect-5heut 1 3630 Cm- 0-H) (GEN) I l l l 4000 v 3000 2000 INFRARED RAY SPECTRUM (6/77") -fIE.

I I l 0 0.5 /.0 /.5 2.0

BONDED WATER PERCENTAGE (70/ /N VEN TORS H/DETO SEK/GUCH/ YASUO MA TSUMURA KOJ/RO ARA/ KUN/O MARU YAMA M/ TSURU WAK/ 7'AN/ GENT United States Patent flice 3,784,666 PROCESS FOR PRODUCING ACRYLIC FIBERS I-Iideto Sekiguchi, Yasuo Matsumura, Kojiro Arai, Kunio Maruyama, and Mitsuru Wakitani, Okayama, Japan, assignors to American Cyanamid Company, Stamford,

Conn.

Filed June 8, 1971, Ser. No. 151,040 Claims priority, application Japan, Aug. 8, 1970, 45/69,481 Int. Cl. B29c 25/00; D01f 7/00 US. Cl. 264-234 10 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a process for producing acrylic fibers having improved elastic recovery properties. More particularly, this invention relates to a process for producing acrylic fibers having increased amounts of chemically bonded water therein whereby remarkable improvements in elastic recovery and hand are obtained.

Acrylic fibers obtained from copolymer in which acrylonitrile predominates have desirable properties such as dyeabilit'y, bulkiness, and hand and, as a result, have developed wide utility in applications as clothing, both outerwear and underwear, and as bed clothes. -In such uses, however, certain property modifications are desirable. In particular, elastic recovery property improvements are desirable, particularly in utilizations where direct body contact is made such as in underwear and bed clothes, in order to expand use of acrylic fibers for such products.

Certain procedures are known for obtaining acrylic fibers with improved elastic recovery. Such procedures involve selection ofspecific polymers of limited choice, variation of copolymer composition, crosslinking of the fiber, and increasing the degree of orientation by adjusting such spinning conditions as stretching and relaxation. By such procedures, although elastic recovery increases to some extent, other rfiber properties such as strength and elongation are reduced. As a result, the known procedures have not been widely accepted.

Under conventional processing conditions, acrylic fibers after being spun are washed with water, stretched, collapsed, relaxed, and then rapidly dried so as to reduce water content of the fiber to below 1% by weight thereof. Such drying procedure results in low values for elastic recovery and the commodity value of the fiber is low. On the other hand, when the fiber has a high Water content associated therewith, the elastic recovery is poor because of the plasticizing action of the water contained therein.

The main object of the present invention is to provide a process for improving the elastic recovery, bulkiness, and hand characteristicsof acrylic fibers without causing losses in desirable fiber properties. Other objects of the present invention will become clear from the discussion which follows.

In accordance with the present invention there is disclosed in a process for producing acrylic fibers wherein a solution of an acrylonitrile polymer is wet-spun into filaments, the filaments are washed with water, the washed filaments are stretched, the stretched filaments are collapsed, and the collapsed filaments are relaxed and dried, the improvement which comprises conditioning the thusobtained fibers at a temperature in the range of about 30 to 80 C. and at a relative humidity in the range of 3,784,666 Patented Jan. 8, 1974 about 70% to 98% for at least about 7 minutes whereby the amount of water chemically bonded to the nitrile groups is at least 0.5% by weight, based on the weight of the fibers, and the ratio of bonded water to total water in the fibers is at least 35%. When conventionally prepared acrylic fibers are conditioned in accordance with the process of the present invention, substantial increases in elastic recovery properties thereof are obtained while other fiber properties are retained at desirable levels. In addition to increases in elastic recovery properties, improved bulk and hand characteristics are also obtained.

Although the present inventors do not wish to be bound by any particular theoretical considerations, it is their feeling that changes in the nature and amount of water present in the fibers are responsible for the improved elastic recovery properties obtained. Thus, the inventors have observed that water present in the fiber is of two types, bonded water and physically adsorbed, but unbonded, water. The bonded water is chemically bonded to the nitrile groups whereas the physically adsorbed water is not engaged in chemical bonding. The conditioning treatment of the present invention increases the content of chemically bonded water to at least 0.5%, by weight, based on the total weight of the fiber and produces a ratio of bonded water to total water of at least 35%. It is thought that, when the fiber is treated to produce the moisture relationships indicated, the bonded water involves adjacent polymer chains, as in the crosslinking of wool by hydrogen bonds, and the result is an improvement in elastic recovery properties of the fiber.

Acrylonitrile polymers useful in producing fibers in accordance with the present invention are polymers and copolymers in which acrylonitrile is the major component. In particular, polyacrylonitrile and a copolymer of at least 70% acrylonitrile and the balance one or more vinyl monomers copolymerizable therewith, as are well known, are preferably employed. Such polymers are obtained by conventional procedures, such as by solution or suspension polymerization. Spinning solutions of such polymers are obtained using suitable polymer solvents, which include organic solvents such as dimethyl formamide, dimethyl acetamide, dimethyl sulfoxide, and ethylene carbonate, and concentrated aqueous inorganic salt solutions such as aqueous solutions of sodium, ammonium, and calcium thiocyanates. Thus, the fiber-forming acrylonitrile polymers and spinning solutions thereof are those conventionally employed in spinning acrylic fibers.

In preparing acrylic fibers from the spinning solutions, conventional wet-spinning procedures are employed. Such procedures include the steps of spinning the polymer soluiton into a suitable coagulant for the polymer, washing the filaments thus obtained in water, stretching the washed filaments for orientation, collapsing the stretched filaments, and relaxing and drying the collapsed filaments. In carrying out the process of the present invention, these basic conventional processing steps are carried out without essential change. In drying the fibers, water may be removed in one or more stages, if desired. In a staged drying procedure, for example, one would reduce the total water content to 10% to 15%, by weight of the fibers, in a primary stage and, in a secondary stage, would further reduce the total water content to the standard moisture regain normally associated with the fiber or to a value below the standard moisture regain.

The conditioning treatment of the present invention is carried out as described above. The treatment may be applied to fibers in the form of a continuous tow or to staple fibers cut to specified length. In addition, it may be applied to fibers in the form of spun yarn or woven or knited fabrics. In such fiber product, acrylic fibers may be present alone or may be present in blends with wool, cotton or other fibers wherein such blends acrylic fibers constitute the major component.

In the accompanying drawings, FIG. 3 represents a plot of elastic recovery against the temperature at which the fibers are conditioned. From the figure, it can be readily seen that the temperature effective in improving elastic recovery properties of acrylic fibers is in the range of 30 to 80 C. At temperatures above 80 C., which is above the secondary transition range, elastic recovery improvements are interfered with due to molecular chain alterations accompanying the high temperatures. At temperatures below 30 0., increases in bonded water content are insutficient to result in improved elastic recovery properties.

With respect to the influence of relative humidity values on the elastic recovery properties obtained under the temperature conditions specified above, it is to be noted that relative humidity values in the range of 70% to 98% must be employed. If the relative humidity value is below about 70%, there is obtained no improvement in bonded water content of the fibers. In fact, at relative humidity values below about 70%, there is observed a loss in bonded water content and in total water content and elastic recovery properties are impaired. On the other hand, if the relative humidity value is above about 98%, such as is obtained with saturated or supersaturated water vapor, the increase in water content of the unbonded type is so great as to require an additional drying step subsequent to the conditioning step and thus complicates the process unnecessarily. The total amount of water present in such case interferes with improving elastic recovery.

In carrying out the conditioning treatment, longer conditioning times lead to greater improvements in elastic recovery properties. A conditioning time of at least seven minutes is required to obtain a practical improvement in elastic recovery properties within the specified range of temperature and humidity values. Preferably the treatment time is at least ten minutes. Preheating of the fibers at a temperature in the range of 30 to 80 C. may be carried out at relative humidity values less than 70% before the conditioning treatment is carried out, if desired. The result of such preheating is to reduce the content of unbonded water in the fiber and to reduce the time duration of the conditioning step that leads to improved elastic recovery properties. The conditioning treatment of the present invention may be carried out efiectively using a wide variety of equipment. For example, batchtype and continuous-type dryers adjustable to fixed temperature and humidity conditions are suitable.

In carrying out the present process, it is necessary that the conditioning step produce in the treated fiber a bonded water content of at least 0.50%, by weight, based on the total weight of the fiber, and a ratio of bonded water to total water weight of at least 35%. If the bonded water content is below 0.50%, the forces holding adjacent molecular chains together is insuflicient to provide the desired improved elastic recovery properties. If the ratio of bonded water to total water content is less than 35%, the excessive amount of unbonded water inteferes with development of improved elastic recovery properties.

The bonded and total water contents as well as the elastic recovery values are determined as next described.

(1) BONDED WATER CONTENT The surface of a fiber to be tested is coated with fluid paraflin. Adsorption strengths at 3630 reciprocal centimeters, representing hydroxyl adsorption, and at 2250 reciprocal centimeters, representing nitrile adsorption are then determined using an infrared spectral analyzer, such as Model 521, manufactured by Perkin Elmer Co. A typical adsorption curve is shown in FIG. 1 of the accompanying drawings. The bonded water content is then determined from the ratio of the measured adsorption strengths. FIG. 2 of the accompanying drawings is a plot of the relationship of bonded water content and the ratio of the hydroxyl adsorption strength D to the nitrile adsorption strength D By determining the ratio of the hydroxyl adsorption strength to the nitrile adsorption strength and locating that value on the line plot, the bonded water content can be determined from the appropriate coordinate.

(2) TOTAL WATER CONTENT The weight W in grams of a fiber sample is first determined. The sample is then dried in a vacuum dryer at 60 C. for 3 hours and the weight W is obtained. The total water content is then determined from the following relationship wherein X, in percent, represents the bonded water content determined above:

Total water content (percent) [100W (100-X)W]:-W

(3) ELASTIC RECOVERY In this procedure, elastic recovery is determined by exerting suflicient tension on a fiber sample to straighten the crimps occurring therein and, after subjecting the fiber to tension for an extended time period with the crimps straightened, determining the extent to which the crimps are recovered. In carrying out the procedure, the fiber is first subjected to a load of 2 milligrams per denier and fiber length L is determined. A load of 50 milligrams per denier is next applied and fiber length L is determined. The sample is then subjected to a load of 20 milligrams per denier for 16 hours, after which the load is removed. The fiber is then allowed to recover for 2 hours. A load of 2 milligrams per denier is applied and fiber length L is determined. A load of 50 milligrams per denier is again applied and fiber length L, is determined. Elastic recovery in percent is then obtained from the following relationship:

Elastic recovery (percent) 100L (L L )+L (Lg-L1) Fibers obtained in accordance with the present invention have greatly improved elastic recovery compared with conventional acrylic fibers, and the present fibers maintain this improved property even under high temperature and humidity conditions normally encountered in use, i.e. temperatures of 30 C. to 40 C. under ambient humidity conditions. Additionally, desirable elastic recovery and soft hand characteristics are reflected in clothing, bed clothes, and underwear made therefrom.

At the same time, desirable fiber properties such as dyeability, strength, and elongation are maintained at values which are at least equal to those of conventional acrylic fibers. Thus, the fibers treated in accordance with the present invention obtain property superiority without sacrifice of desirable properties.

Added features of the present invention are reflected in the facts that no special treating agents are required and that the process is carried out in a simple fashion. The present invention thus provides an economical process that can be readily carried out on a commercial scale.

The invention is more particularly illustrated by the examples which follow in which the parts and percentages are by weight unless otherwise specifically indicated.

EXAMPLES 1-4 Following conventional procedures two spinning solutions were prepared using concentrated aqueous sodium thiocyanate as polymer solvent. The first polymer was a copolymer of 9.8% methyl acrylate, 0.2% sodium methallyl sulfonate, and acrylonitrile. The second polymer was a copolymer of 11% vinyl acetate and 89% acrylonitrile. The spinning solutions were wet-spun into composite fibers following conventional procedures including the steps of water-washing, stretching, collapsing, relaxing and drying. The fiber obtained was cut into staple lengths of 76 millimeters and represented a fiber of 6 deniers. The fiber as obtained is represented as comparative Example A in Table I below. Portions of the fiber were subjected to con ditioning at various temperatures and relative humidities. The conditioning treatments as well as fiber properties re sulting therefrom are given in Table I, which follows.

6 cording to the process of the present invention exhibits superior bulk retention to that obtained with fibers not conditioned by the process of the present invention.

TABLE I Ratio of Treating conditions bonded Bonded H to Elastic Strength Elonga- Temp., Percent Time, H2O total H3O, recovery, grams] tion, Example No. C. R.H. min percent percent percent 1 denier percent Comparative A Untreated 0. 39 10 Comparative B 20 90 60 0.40 47 13 1 90 60 0. 66 40 17 55 90 60 0. 60 36 21 70 90 60 0. 64 37 22 100 90 60 0. 60 38 13 6E 90 0. 59 42 20 Comparative D- 65 40 60 0. 39 45 12 1 Tested at 35 0. and 90% 11.11. I Preheated 5 minutes at 60 C. and 65% relative humidity (R.H.)

It can be seen from the results given in Table I, that the fibers of comparative Examples A and B contain insnfiicient bonded water and, as a result, show low elastic recovery values. The fibers of Examples 1-4, inclusive each show a value of bonded water of at least 0.50% and significantly improved elastic recovery properties. It is to be noted that the strength and elongation properties of the fiber of Example 2 were equal to those of the untreated fiber of comparative Example A, thus showing that the conditioning treatments have no adverse efiects on such properties. In Example 4, the untreated fiber was first preheated for 5 minutes at 60 C. and 6-5 relative humidity and then subjected to conditioning as in Example 2, but for a. reduced time period. This example thus shows that preheating under conditions outside those of the conditioning step of the present invention can be used to reduce the duration of the conditioning step.

Comparative Example C shows that when the relative humidity during conditioning is too high, the desired increase in elastic recovery is not obtained. Comparative Example D shows that when the relative humidity during conditioning is too low, the desired increase in elastic recovery is not obtained.

EXAMPLE 5 The fiber represented as comparative Example A was again employed. A portion of this fiber was conditioned for 60 minutes at 60 C. at a relative humidity of 90%. The conditioned fiber was carded, cut, piled into a square of 8 centimeters on a side in sufiicient amount to obtain a weight of 6.4 grams. In a similar manner, squares were prepared from the fiber of comparative Example A (no conditioning employed) and from the same fiber conditioned under the conditions of this example but for a time period of only 2 minutes, the fiber being designated comparative Example E. The conditioning variables and fiber prop- EXAMPLE 6 A spinning solution was prepared following conventional procedures using concentrated aqueous sodium thiocyanate as the polymer solvent. The polymer was a copolymer of 9.8% methyl acrylate, 0.2% sodium methallylsulfonate, and 90% acrylonitrile. This solution was wet-spun following conventional procedures, including the steps of waterwashing, stretching, collapsing, relaxing and drying to obtain a fiber of 3 deniers. A portion of the fiber thus obtained was subjected to secondary stretching under the influence of dry heat in accordance with conventional procedures to obtain a fiber having a shrinkability of 20%. A fiber blend was prepared employing of the fiber originally obtained and 40% of the fiber treated to produce the shrinkability of 20%. The blend was mixed and spun to produce a bulky yarn according to conventional procedures. The yarn thus obtained was hank-dyed and fashioned into a plain knit sweater (14 gauge). The sweater was treated for 60 minutes at 60 C. and at 90% relative humidity in accordance with the present invention. Fibers of the treated sweater showed a bonded water content of 0.59% and a ratio of bonded water to total water of greater than 35%. The sweater exhibited a softer and more wooly hand as well as increased elastic recovery compared to an identical sweater which was not subjected to the conditioning treatment.

We claim:

1. In a process for producing acrylic fibers wherein a solution of an acrylonitrile polymer is wet-spun into fila ments, the filaments are washed with water, the washed filaments are stretched, the stretched filaments are collapsed, and the collapsed filaments are relaxed and dried, the improvement which comprises conditioning the thusobtained fibers at a temperature in the range of about 30 C. to 80 C. and at a relative humidity in the range of erties are given in Table II, which follows. 40 about 70% to 98% for at least about 7 minutes whereby TABLE II Ratio of Treating conditions bonded Bonded H20 to Bulki- Bulk re- Temp., Percent H 0 total H20 ness, tentlon, Example No. C. R.H. Time percent percent emi /gm. percent Comparative A Not treated 0.35 39 76 30 Comparative E... 60 90 2 0.40 36 76 33 5 60 0.61 37 76 45 the amount of water chemically bonded to the nitrile groups is at least 0.5% by weight, based on the total weight of the fibers, and the ratio of bonded water to total water in the fibers is at least 35% 2. The process of claim 1 wherein the drying step is carried out under conditions which produce a moisture regain less than the standard moisture regain associated with said fibers.

3. The process of claim 1 wherein said fibers are monocomponent.

4. The process of claim 1 wherein said fibers are com- The data of Table H shows that fiber conditioned acposite fibers.

5. The process of claim 2 wherein said fibers are monocomponent.

6. The process of claim 2 wherein said fibers are composite fibers.

7. The process of claim 1 wherein conditioning is carried out for at least 10 minutes.

8. The process of claim 2 wherein conditioning is carried out for at least 10 minutes.

9. The process of claim 1 wherein said conditioning step is carried out at a temperature in the range of 40 to 70 C. and at a relative humidity of about 90%.

10. The process of claim 2 wherein said conditioning step is carried out at a temperature in the range of 40 t0-70 C. and at a relative humidity of about 90%.

References Cited UNITED STATES PATENTS 2,499,477 3/1950 Field 8--130.1 2,984,912 5/1961 Robertson et a1 264182 3,330,898 7/ 1967 Hurley et a1 264---182 3,433,866 3/ 1969 Lombard et al 264-182 3,472,017 10/ 1969 Nakagama et a1 57140 3,451,140 6/1969 Nakagama et a1 34-12 3,514,512 5/ 1970 Kikuchi et a1. 264-182 FOREIGN PATENTS 13,698 7/1965 Japan 264-182 6,213 4/ 1966 Japan 264-182 JAY H. WOO, Primary Examiner US. Cl. X.R. 

